Comment by njtransit

The issue is that almost all human behavior is correlated and, even if you have an easy-to-see [sic] method of action, e.g. “brain gunk”, that doesn’t automatically negate a nearly-infinite set of other possible causes from correlated behavior. Just a random example: those with high stress probably sleep poorly. You can think of a number of possible explanations that link high stress to shorter lifespans: more likely to commit suicide, more fat retention, less time for healthy activities, etc.